1. Field of the Invention
This invention relates generally to an improved rotary valve in which a diverter disk seats against a generally U-shape seating frame. More specifically, it relates to the use of such improved valve in a heavy duty fluid flow diverter apparatus for reversing fluid flow through a process loop. Such apparatus is particularly well adapted for alternating the direction of flow of the cooling water in heat exchange systems that utilize the pressure of the cooling water to propel brushes or other cleaning elements back and forth through heat exchange tubes to remove scale.
2. Description of the Prior Art
Air conditioning or refrigerating systems that utilize alternate compression and expansion of a refrigerant gas require means to remove heat from the refrigerant following the compression cycle. Commercial systems commonly employ tubular heat exchangers for this purpose.
A typical tubular heat exchanger for a commercial air conditioning system is an elongated vessel having bundles of heat exchange tubes supported at their ends by tube sheets that separate the exterior surfaces of the tubes from the water boxes at the ends of the vessel. The interiors of all of the tubes are open to an individed water box at one end of the vessel and half of these tubes are open to each chamber of the divided water box at the other end of the vessel. The compressed refrigerant which is to be cooled or condensed flows over the exterior surface of the tubes in the space between the tube sheets. Cooling water enters one chamber of the divided water box, passes through the tubes that are open to that chamber into the undivided water box and then through the remaining tubes into the second chamber of the divided water box. Cooling water thus enters and leaves the heat exchanger vessel at the same end.
Since raw water or inadequately demineralized water usually is used, it is necessary to frequently remove precipitated minerals or scale from the inside of the heat exchange tubes in order to prevent corrosion and heat transfer inhibition. A common method of doing so is to utilize the cooling water pressure to drive a brush or other cleaning element through each tube in the bundle. As described in U.S. Pat. No. 3,319,710, each tube in the bundle terminates at each end in a cage, one of which contains the tube brush. When it is desire to clean the tubes, the direction of flow of the cooling water is reversed, driving the brushes through the tubes and into the cages at the opposite ends of the tubes.
Reversing the direction of flow of the cooling water can be accomplished by a wide variety of 4-way valves, illustrative of which is the valve shown in U.S. Pat. No. 3,307,583, which varies the direction of flow by rotation of a diverter disk between seated positions abutting generally U-shape resilient sealing strips that are fixedly attached to the inside of the valve casing. A major disadvantage of such prior art 4-way valve is the fact that, under heavy duty usage, erosion or distortion of the seating surfaces on the resilient sealing strips, as well as on the disk, causes excessive leakage and the valve frequently must be taken off line for tedious repairs or replacement. Another disadvantage of such valve is the fact that the supply and return ports are on opposite sides of the casing and are separated by the reversible flow ports. This requires that the valve be surrounded by a maze of pipes and elbows in order to connect to the generally parallel and closely spaced reversible flow lines emerging from the heat exchanger, as well as the water supply and return lines, which also usually are parallel and closely spaced. When the available space in the vicinity of the valve is limited, as it commonly is, such tangle of external piping can obstruct access to the valve and may be a physical hazard to workers in an extremely cramped working area.
One means of solving this problem is set forth in U.S. Pat. No. 3,973,592. This patent describes a 4-way valve in which a plug type diverter is rotatable within four circumferentially spaced cage bars that form pairs of opposed seats for sealing engagement with the two edges of the valve plug to connect various chambers within the valve housing with upstream and downstream fluid flow lines, depending on the rotary position of the valve plug.
While this valve effectively eliminates the need for an external maze of pipes and elbows, it has a number of serious disadvantages. The use of cage bars for plug sealing requires extremely close tolerances to prevent excessive leakage and the tortuous flow paths around the various walls and partitions within the valve housing results in a significant fluid pressure drop. The utilizationi of numerous walls and partitions within the valve housing also creates a complex structure that is difficult and expensive to manufacture and that often necessitates removal of the diverter from the line for extensive periods for repair or other service. This service difficulty can be particularly troublesome when abrasive solids occasionally become suspended in the fluid or when the diverter is used in seasonal applications, such as in an air conditioning system, where the plug valve often is found to be jammed after a period of disuse.
The need for an external maze of pipes and elbows to connect the diverter to the generally parallel incoming and outgoing fluid lines also can be avoided by the compact and jam resistant diverter described in copending application Ser. No. 829,297. This diverter utilizes a 4-way valve comprising a pipe casing containing an oval rubber edged butterfly disk having its short axis diametrally positioned within the pipe casing so that the edge of the disk is seatable in two positions against the inner wall of the casing when the disk is rotated about its short axis. Two ports are located at opposite ends of the pipe casing and two additional ports are concentrically positioned in the wall on opposite sides of the disk, so that the end ports alternately can be placed in fluid communication with either of the side ports by turning the disk from one seated position to the other. A housing which encloses the 4-way valve has pairs of closely spaced orifices distally positioned in its wall for connection with parallel external fluid lines. Separate fluid conduits connect these orifices to the valve ports with one or two of these conduits being free space in the interior of the housing.
Because of the rubber to metal seal created by the rubber periphery of this oval disk seating against the pipe casing, the leakage rate is far less than the metal to metal seals of earlier diverters. However, erosion of the rubber or distortion of the disk sometimes occurs in heavy duty applications due to high fluid pressures or the introduction of extraneous solids, and the resulting increased leakage necessitates removal of the disk for repair or replacement.